The present invention relates generally to vehicle heating, ventilation and air conditioning (HVAC) systems having multiple evaporators.
Vehicle HVAC systems may have multiple evaporators. For example, a vehicle may have a front HVAC module, a rear HVAC module and a battery pack cooling module, with each having a refrigerant loop directing refrigerant (including oil) through its respective evaporator. Such HVAC systems have different refrigerant flow rates in each loop that depend upon the particular cooling needs for that loop at any given time. That is, there may be times when the cooling demand from the front HVAC module is high and the demand from the rear HVAC module is low (or none) if there are no passengers in the rear of the passenger compartment. Moreover, the battery pack cooling loads may be significantly less than the passenger cabin cooling loads under some vehicle operating conditions, while under other operating conditions, there may be no passenger cabin cooling loads even though cooling of the battery pack may be needed.
Those loops experiencing low (or no) refrigerant flow over a period of time have the potential for oil accumulation in that loop. Moreover, the packaging space and line routing needed to supply refrigerant flow through these multiple loops to three evaporators, which may be spaced apart by significant distances in some vehicles, may exacerbate the oil accumulation concern by increasing the likelihood of oil accumulation in some lines.
Too much oil accumulation in the refrigerant lines increases the likelihood of increased compressor wear or possible failure if sufficient oil is not returned to the compressor. One may counter this by increasing the oil charge in the system. However, system performance may be reduced since additional oil in the evaporators may reduce the evaporator efficiency. And, the extra oil in the system will increase the cost of the HVAC system.